Low drag flameholder capable of flutter during operation



United States Patent C LOW DRAG FLAMEHOLDER CAPABLE .OF FLUTIER DURINGOPERATION Robert A. Arnoldi, Elmw'ood, Conn.,assignor toUnited AircraftCorporation, East Hartford, Conn., a corporation of DelawareApplicafion'necember 14, ,1956, serial No. 628,427 Vs claims. (ci.60.43952) `This invention relates to combustion chambers. and :amorespecifically to flameholder mechanisms for high flow velocities in suchcombustion' chambers.

It is an object of this Ainvention toprovide-a ilame- A:holder mechanismwhich provides a maximum ofturbu- Vlence when in operation and a minimumof drag when --not in operation.

It is a further object of this invention to provide a A fiameholdermechanism ofthe `typeA described without resorting to the heavystructures attendant with use of, 'for example, retractibleilameholders.

It is a still further object ofV this -invention to utilize streamlinedilameholder elements which normally present Fig. 2 is similar to Fig. lwith the flameholder parts in the operative position;

v Fig 3 is an enlarged detailedcross-section illust-rating the lmountingfor -the Vilameholder` elements;Y and i Fig. 4 is a partialcross-section illustrating a means for exciting oscillation ofv thelfla'ineholderele'ments.

Referring to Fig. 1, arturbojet poweryplant is generally indicated at"10as having a compressorIZ, a burner v14, a `turbine section---16,-anlafterbur'nerg-v 'section 18,"and an lexhaust -nozzleAf20which-may havee'its'area Yvariedfby a plurality v'of clamshell-type#lids -22. The fuel Vdistributing power plant at a point downstream"ofthe burner 14 and turbine.16,.toprovideafterburningin `the powerhr1plant and additional thrust.

A ameholder mechanism 30 is provided in the afterburner section 18 andcomprises a supporting bar 32 which carries a plurality ofairfoil-shaped members 34 which span the `afterburner duct and extendtransversely of the axis of flow through the afterburner. Each of thestreamlined members 34 is mounted on a shaft 40 (Fig. 3) which ispivotally mounted in a slot 42 in the member 30. The shaft 40 is xed toone end of a coil spring 44 which has its other end xedly mounted at 46to the transverse member 30. With this type of mounting the airfoilmember 34 is free for limited pivotal move.- ment about the shaft `40,thus providing airfoils which can simultaneously oscillate about aspan-wise axis, and execute lateral oscillations transversely of theaxis of ow through the afterburner. An alternate coniiguration may behadby replacing the slot 42 by a simple member 26 is providedtpinjecadditional fuel into the V `pivot as shown in Figs. 1 and 2, sothat only Patented Octal?, 1959 pivotal oscillations arepermitted.

As seen in Fig. 1, a locking member v48 is provided with a plurality ofnotches or detents 50 (Fig. 3) which are intended to engage the leadingedge of eachv of the streamlined members 34. The locking member `48-isconnected by a linkage 52 to a servo cylinder piston combination 54which can be moved fore and aft bylilid under pressure with any suitablewell-known control. The link '52 is also connectedY to a link 56,carriage '58 and linkage60 which connects to the eyelids 22onthe exhaustnozzle. Thus, rearward movement of the cylinder piston combination A54will engage the member 48 and the detents 50 with the leading edge ofthe streamlined members 34 and simultaneously decrease the area of thenozzle 20 by moving the .eyelids 22 to the position shown in Fig. l.Slotted guides 61 suitably engage the supporting bar 32 adjacent itsextremities.

As seen in Fig. 2, the cylinder piston combination has been actuatedtoward the left, thereby moving the transverse locking member 48 out ofengagement with the streamlined members 34, so that they will be freetooscillate about their pivot shaft 40 (see Fig. 3 also). In this positionthe airfoil `members'34 will oscillate'in the manner shown, .therebycreating a turbulencedownstream thereof to provide adequate ilameholdingoperation.

When the detent l48 is engaged, some motion'of the airfoils about thepoints of engagement with the detent is possible where both a pivot 40and slot `42 are-.provided. However, flutter about thesepoints is highlyimprobable.

At the same time that the locking member 481has'5been .moved to the leftout of engagement with the streamlined .members 34, the eyelids 22.areopened to-providea'n increased exhaust nozzle area to accommodatetheadditional mass` flow during theV afterburning operation. =fIt isthus apparent, with the position of the ameholder .elements 34. as shownin Fig. l, avery minimum ofdrag is 4present 4during thenon-afterburningoperatiomrthus maximum power plant efficiency is.obtained. Onthe 4other hand, in .the position fshownin `Fig. 2 ladequateturbulence is provided to obtain the necessarygamehold- :ingfortheiafterburnergoperation;

. As seen in Fig. 4, a:secondary fuel adistrihutorgline() vrnay`beprovided with .a plurality.-.of nozzles 5.62:. and 64 -vwhich .cause:ffuel tofimpinge :on nthe ,upperrand lower ytrailingedge surfacesuoflhe.streamlined membersfl.

This` presents. a well-'known `unstable configuration :and willcausetheairfoil to-.oscillate at adesirable frequency.

Thisico'nguration is intended to, app1y1when..the nature `of the.particular afterburner designdoesinotzpermit selfiexcited.aerodynamic.` itlutter .but requiresV an additional vmechanism togcausevibration. Itishouldbetpointedtout that the springs 44 shown in bothFigs. 3 and 4 are intended to regulate or predetermine the naturalfrequency of the torsional vibration of the streamlined elements 34. Itis apparent that as a result of this invention a simple yet highlyeiicient ilameholder mechanism has been provided which will cause aminimum drag when not operating and will hence have the least possible,adverse effect on normal engine operation. At the same time when it isvdesirable to provide flameholding, ecient ilameholding action isprovided. Furthermore, the mechanism for operating or disabling theameholder mechanism is con# nected to operate simultaneously with theelements which' vary the area of the exhaust nozzle'.

Although only one embodiment of this invention has been illustrated anddescribed herein, it Will be apparent that various changes andmodiiications may be made in the construction `and arrangement of thevarious parts without departing from the scope of this novel concept.

, g 3 What it is desired by Letters Patent is: l. I n =a combustionchamber having high velocity gases flowing therethrough, means forintroducing fuel into said' 'combustion chamber,"V llameholderf'means`for. stabilizing the flame in said combustion chamber includinga'pl'urality ofstreamlined members extending transversely of the. axis vof flow,Y throughV the combustion chamber, each .of said L Amembershaving a spanwise axis, and means for mounting I said members forVrelatively free Vbut limited pivotal movement aboutl said spanwise axis.and limited movement transverselytof said axis.

2. `In a combustion chamber having high velocity gases owingtherethrough, means for introducing fuel into said f. combustion chamber,ameholder means for stabilizing thefame in said combustion chamberincluding a plurality fof streamlined members extending transversely oftheV axis of flow through the combustion chamber, each of Ysaid membershaving a spanwise axis, and means for f` mounting said members forrelatively free butlimited i pivotal movement about said-spanwise axisand limited movement transversely of said'axis, and means for refstraining said' members-.against movement. 1

3.V In a combustion chamber having high velocity gases flowingtherethrough, means for introducing fuel into said combustion chamber,ameholder means `for stabilizing the flameY in said combustion chamberincludingA aY plumembers for restraining said members against movementabout saidaxis, and-means for simultaneouslyreducing the area of saidnozzle and engaging said restraining means.

6. In a combustion chamber having high velocity gases flowingtherethrough, an exhaust nozzle receivingV iluid from said combustionchamber, means for varying the area of said nozzle, means forintroducing fuel into said rality of streamlined members extendingtransversely of cluding a plurality ofV streamlined membersextendingtransversely of the axis of ow through the combustion chamber, each ofsaid members having a spanwise axis,

i means `for mounting said members for pivotal movement about said axisincluding a spring, means .engageable Withsaid members for restrainingsaid members against movement aboutsaid axis, and means kfor engagingsaid restraining means. Y i 1' 5. In a combustion chamber having highvelocitygases flowing therethrough, an exhaust' nozzleY receiving iluidfrom said Vcombustion chamber, means `for varying the area ofsaidnozzle, rmeans for'introducing fuel introl said .combustion chamber,flameholder means for stabilizing the flame in said combustion chamberincluding' a plurality of streamlined members extending transversely ofthe axis of ow through the combustion chamber, each of said membershaving aY spanwise axis, means' Vfor mounting said' members for pivotalmovement about said axis including a spring bias, means engageable withsaid combustion chamber, flameholder means for` stabilizing the`ame insaid combustion chamber including a plurality of, streamlined members ofairfoil shape extending transversely of the axis of flow through thecombustion chamber in substantial alignment with the fluid stream,

means for mounting said members for pivotal movement` about a spanwiseaxis including a spring for biasing movement of said members about saidaxis, detent means en-V gageable With said members for restraining saidmembers against movementab'out-said axis, and means for simultaneouslyreducing the area of said nozzle 'and engaging said restraining means.,V 7. In a combustion chamber having high velocity gases iflowingtherethrough, means for introducing fuel into said combustion chamber,flameholder means for stabilizing the `flame in said combustion chamberincluding a plurality of streamlined members .extending transverselyofthe axis'of owthrough the combustion chamber, each of saidmembershaving a spanwise axis, and Vmeans kfor mounting said members forlimited and substantiallyunrestrained oscillatory pivotal movement aboutsaid span- 'Wise axis as a result of the gas stream flowing thereover,

j and Vmeans `for restraining said members againstmovement about saidaxis in a streamlined position relative to theV gases flowing by saidmembers. V Y Y 8. In a combustion chamber having high velocity gasesflowing therethrough, means for introducing fuel into said f combustionchamber, ameholder means for stabilizing the iiame infsaid combustionchamber includinga pluralityv of streamlined members extendingtransversely of the V,axis of ow through Vthe combustion chamber,reach.V

of said members having a spanwise axis, and meansifor mounting saidmembers for limited and substantially unf restrained oscillatory-pivotalmovement about'said span- Wise axis, means separate-from the gas streamowing throughrtheV combustion chamber for excitingl sadoscillatorymovement, and means fork restraining said members f againstmovementaboutsaid raxis-in a streamlined posi- 'fffj '.NiTED'sTATEsPATENTS1,237,779A iHedn'ck im Aug. 21,- 1917 v2,6%,709 oulianoff Dec. 14,1954

` tion relative to the gases flowing by said-members'.`-

References Cited in the le of this patentv 27,835,108 .Y Karen 'May2o,195sv Y vi-'onniGN PATENTS i

